多层微穿孔板结构声学性能计算方法对比分析

计算多层微穿孔板结构声学特性方法传统主要用声电类比法,目前出现阻抗转移法和传递矩阵法,对比分析这三种计算方法,同时进行相应的实验验证。结果表明:阻抗转移法和传递矩阵法实质上是相同的,这两种方法计算结果与实验结果吻合良好。声电类比法在空腔较大时计算结果偏离实验值,原因是声电类比法采用集总参数分析,计算多层结构时,空腔单元只考虑声顺,忽略声质量,导致误差。阻抗转移法和传递矩阵法不存在这一误差,计算准确。     

计及孔间相互作用的微穿孔板吸声特性研究

计算微穿孔板吸声系数时,假设孔间的相互作用可以忽略。计算具有不同直径微孔的穿孔板吸声系数并提高其计算精度,孔间的相互作用不能再忽略。在马大猷、Melling(梅尔林)等前人研究的基础上,根据声波辐射和传播原理,分析微孔之间的相互作用,通过修正微孔的实际等效长度,得到计及孔间相互作用微孔板吸声系数模型,并进行理论计算和实验测试。研究结果表明:影响微穿孔板吸声系数除结构参数外,还应考虑孔间的相互作用;计及微孔板各孔间相互作用,能提高共振频率、吸声系数理论值的计算精度,计算值逼近实验测试结果。     

水下弹性微穿孔吸声结构吸声系数研究

利用模态叠加法建立了水介质微穿孔板的数学模型,基于声电类比法得到其等效电路模型.研究了弹性微穿孔板和弹性背腔对垂直入射吸声系数的影响.与空气介质中的微穿孔板不同,水下微穿孔板因结构阻抗不足,难以取得满意的吸声效果,为此提出了增强型微穿孔吸声结构,并在水介质阻抗管内对理论结果予以验证.结果表明,随着增强型弹性微穿孔板弯曲...     

水下微穿孔吸声体结构设计与试验研究

根据马大猷院士的微穿孔板(MPP)理论,提出在可设计的夹芯复合隐身结构的空腔中附加微穿孔板层的水下微穿孔吸声体。基于微穿孔板的精确计算理论及水下声隐身结构的特点,考虑空腔深度、穿孔板厚度、穿孔直径及穿孔率等对微穿孔板吸声性能的影响,对水下微穿孔吸声体进行了结构设计。利用脉冲声管法对水下微穿孔吸声体试样的吸声系数进行了测量,结果表明:水下微穿孔吸声体有效地拓宽了低频吸声频带,其微穿孔板结构参数的影响规律也与理论分析一致;对于多种吸声机理并存的水下微穿孔吸声体的空腔个数、形状及谐振特性等也是影响吸声性能的重要因素,在实际的工程应用中必须结合所关心的频带对水下微穿孔吸声体进行匹配优化设计。      

穿孔率和穿孔直径耦合下微穿孔板吸声体整体吸声性能

微穿孔板几何参数的耦合性及其对整体吸声性能的影响,对于设计微穿孔板吸声体和优化其工作性能具有指导作用.根据微穿孔板吸声体基本理论,研究了穿孔率和穿孔直径双参数耦合作用下微穿孔板吸声体的整体吸声性能.穿孔率和穿孔直径之间的耦合性与其本身取值密切相关,而与板厚和板后腔深无明显关系;在穿孔率-穿孔直径参数域上,吸声体存在吸声...     

Advances in micro-perforated panel absorbers

Theoretical and experimental investigations on the performance of micro-perforated -panel absorbers are reviewed in this paper. By reviewing recent research work, this paper reveals a relationship between the maximum absorption coefficient and the limit of the absorption frequency bandwidth. It has been demonstrated that the absorption frequency bandwidth can be extended up to 3 or 4 octaves as the diameters of the micro-holes decrease. This has become possible with the development of the technologies for manufacturing micro-perforated panels, such as laser drilling, powder metallurgy, welded meshing and electro-etching to form micrometer order holes. In this paper, absorption characteristics of such absorbers in random fields and in high sound intensity are discussed both theoretically and experimentally. A new absorbing structure based on micro-perforated-panel absorbers demonstrate experimentally high sound absorption capability. This review shows that the micro-perforated-panel absorber has potentials to be one of ideal absorbing materials in the 21st century.     

Acoustic properties of micro-perforated panel absorber having arbitrary cross-sectional perforations

Micro-perforated panel absorber is used in many noise control applications as a next-generation absorbing material. Perforation shapes of micro-perforated panel studied are usually circular in the past. However, in practice, the perforations are often non-circular or irregular shape due to manufacturing techniques. Sound absorption coefficient and absorption bandwidth of the micro-perforated panel absorber may be further improved, when the perforations in shape are changed. In view of the existing exact solutions of sound propagation in tubes, the simple formulas of specific acoustic impedances of the tubes for triangle and square cross-sectional perforations are derived. Mass reactance end correction of the micro-perforated panel is obtained based on the sound radiation of a shaped piston. The specific acoustic impedance ratio of the micro-perforated panel absorber is calculated and analyzed, which can predict its sound absorption bandwidth. Finally, for closed perforations, the influences of the perforations in shape (including triangle, circle, square and irregular circle) on sound absorption of the MPP absorber are discussed in collaboration with FE simulations.     

微穿孔板吸声结构水下应用研究

马大猷教授提出的微穿孔板吸声结构在空气噪声降低和隔离方面得到了广泛的应用,但未见水下应用的相关研究和报道。本文将空气中微穿孔板理论应用到水中,得到了水下微穿孔板吸声结构的吸声公式。通过理论分析,得出了微穿孔板结构直接应用于水中无法获得宽频吸收的结论。提出了通过匹配液将微穿孔板间接应用到水下的设想。设计了单层板和双层板吸声结构,并对它们的吸声特性进行了理论分析与仿真。结果表明,本文设计的微穿孔板吸声结构在水中能够获得优于空气中的宽频带吸声效果。实验测量了自制的微穿孔板吸声结构,吸声系数的测量值与理论曲线基本吻合,从而验证了理论分析的正确性。     

微穿孔介电弹性体薄膜的吸声性能试验分析*

针对普通薄膜型降噪结构的吸声性能较差和吸声带宽较窄的问题,本文设计了一种微穿孔的介电弹性体薄膜吸声结构。该结构由穿孔的介电弹性体薄膜与背腔组合而成,目的是拓宽介电弹性体薄膜低频率段的吸声带宽。针对微穿孔的介电弹性体薄膜吸声结构,从试验角度分析穿孔薄膜初始厚度、穿孔孔径及穿孔间距对结构吸声性能的影响。分析结果可知：通过适当增加薄膜的初始厚度,薄膜的整体吸声性能得到有效提升,最大可将319Hz吸声频带的吸声系数从0.2提升至0.7;减小薄膜的穿孔孔径能够有效拓宽穿孔薄膜的吸声频带,可使吸声系数0.4以上的吸声带宽由304Hz拓宽至432Hz;适当控制穿孔间距能够达到更好的吸声效果。     

Sound absorption of a double-leaf micro-perforated panel with an air-back cavity and a rigid-back wall: Detailed analysis with a Helmholtz-Kirchhoff integral formulation

So far the electro-acoustical equivalent circuit analysis has been widely used to analyse micro-perforated panel (MPP) absorbers, however, as for the double-leaf MPP the equivalent circuit analysis inevitably includes an approximation. In this paper, the sound absorption characteristics of a double-leaf MPP absorber backed by a rigid wall are analysed by wave theory using Helmholtz-Kirchhoff integral formulation to obtain a strict solution. The present wave theory is experimentally validated with existing measured results. The theory is also compared with the equivalent circuit solutions so that the differences between the two theories appear and the effect of the approximation is clarified. The comparison shows that the difference mainly appears in the vicinity of the resonance peaks: the differences occur in the resonance frequencies and the absorption coefficient at frequencies between the two resonance peaks.     

Sound absorption and transmission through flexible micro-perforated panels backed by an air layer and a thin plate

This paper describes theoretical and experimental investigations into the sound absorption and transmission properties of micro-perforated panels (MPP) backed by an air cavity and a thin plate. A fully coupled modal approach is proposed to calculate the absorption coefficient and the transmission loss of finite-sized micro-perforated panels-cavity-panel (MPPCP) partitions with conservative boundary conditions. It is validated against infinite partition models and experimental data. A practical methodology is proposed using collocated pressure-velocity sensors to evaluate in an anechoic environment the transmission and absorption properties of conventional MPPCPs. Results show under which conditions edge scattering effects should be accounted for at low frequencies. Coupled mode analysis is also performed and analytical approximations are derived from the resonance frequencies and mode shapes of a flexible MPPCP. It is found that the Helmholtz-type resonance frequency is deduced from the one associated to the rigidly backed MPPCP absorber shifted up by the mass-air mass resonance of the flexible non-perforated double-panel. Moreover, it is shown analytically and experimentally that the absorption mechanisms at the resonances are governed by a large air-frame relative velocity over the MPP surface, with either in-phase or out-of-phase relationships, depending on the MPPCP parameters.     

Design of a single layer micro-perforated sound absorber by finite element analysis

Micro-perforated sound absorbers with sub-millimeter size holes can provide high absorption coefficients. This paper presents results of work on the development of an effective single layer micro-perforated sound absorber from the commercial composite material Parabeam^® with micro diameter holes drilled on one side. Parabeam^® is used as a structural material made from a fabric woven out of a E-glass yarn and consists of two decklayers bonded together by vertical piles in a sandwich structure with piles (thick fibers) woven into the decklayers. The paper includes, the analytical model developed for prediction of absorption coefficients, finite element solution using commercial software MSC.ACTRAN and experimental results obtained from impedance tube measurements. A simple optimization is performed based on the developed models to obtain an efficient absorber configuration. It has been anticipated that several different and interesting applications can be deduced by combining structural and sound absorption properties of this new micro-perforated absorber.     

Enhancing the low frequency sound absorption of a perforated panel by parallel-arranged extended tubes

This paper is concerned with the use of a perforated panel with extended tubes (PPET) to improve the sound absorption confined to low frequencies. In comparison with a micro-perforated panel (MPP), the sound absorption can be significantly improved by using the PPET at the expense of the bandwidth of the sound absorption. A particular configuration combining four parallel-arranged PPETs with different cavities is introduced to achieve a wider bandwidth of the sound absorption at low frequencies. The analysis is extended to the combination of three parallel-arranged PPETs and a MPP to further increase the bandwidth of the sound absorption. A theoretical model is described to predict the sound absorption coefficient and the simulated annealing method is introduced to the proposed absorbers, allowing optimization of the overall performance. The theory with experimental validations demonstrates that the proposed configurations offer a potential improvement of more than one octave in the bandwidth of the sound absorption at low frequencies.     

Modeling of micro-perforated panels in a complex vibro-acoustic environment using patch transfer function approach

A micro-perforated panel (MPP) with a backing cavity is a well known device for efficient noise absorption. This configuration has been thoroughly studied in the experimental conditions of an acoustic tube (Kundt tube), in which the MPP is excited by a normal incident plane wave in one dimension. In a more practical situation, the efficiency of MPP may be influenced by the vibro-acoustic behavior of the surrounding systems as well as excitation. To deal with this problem, a vibro-acoustic formulation based on the patch transfer functions (PTF) approach is proposed to model the behavior of a micro-perforated structure in a complex vibro-acoustic environment. PTF is a substructuring approach, which allows assembling different vibro-acoustic subsystems through coupled surfaces. Upon casting micro-perforations and the flexibility of the MPP under transfer function framework, the proposed PTF formulation provides explicit representation of the coupling between subsystems and facilitates physical interpretation. As an illustration example, application to a MPP with a backing cavity located in an infinite baffle is demonstrated. The proposed PTF formulation is finally validated through comparison with experimental measurements available in the literature.     

Experimental investigation of holes interaction effect on the sound absorption coefficient of micro-perforated panels under high and medium sound levels

This paper experimentally investigates the holes interaction effect on the sound absorption coefficient of micro-perforated panels under high and medium sound levels. The theoretical formulations are based on a semi-empirical approach and the use of Fok’s function to model the acoustic surface impedance. For the high sound level regime, an empirical power law involving three coefficients is adapted. It is shown theoretically and experimentally that these coefficients can lead to optimized absorption performance and particularly, a formula relating the critical Reynolds number (Reynolds number value after which the absorption coefficient decreases with the increase of sound level) and the center-to-center distance between the perforations is derived. It is demonstrated that the first coefficient of the nonlinear acoustic resistance strongly depends on the separation distance between the apertures and decreases with a decrease of this latter distance. Analysis of the data reveals the fact that even with Holes Interaction Effect (HIE), the nonlinear reactance dependence on velocity is still very low compared to the resistance-velocity dependence. Four perforated panels of 1.5 mm thickness with different separation distances between the holes (from widely to closely separation) were built and tested. Experimental results performed with an impedance tube are compared with the described model for HIE. To test the dependence of the coefficients on frequency, the experiments are carried out for two different excitation frequencies (292 Hz and 506 Hz). The results can be used for designing optimal perforated panels for ducts, silencers and for the automotive industry.     

Vibroacoustic properties of thin micro-perforated panel absorbers

This paper presents theoretical and experimental results on the influence of panel vibrations on the sound absorption properties of thin micro-perforated panel absorbers (MPPA). Measurements show that the absorption performance of thin MPPAs generates extra absorption peaks or dips that cannot be understood assuming a rigid MPPA. A theoretical model is established that accounts for structural-acoustic interaction between the micro-perforated panel and the backing cavity, assuming uniform conservative boundary conditions for the panel and separable coordinates for the cavity cross-section. This model is verified experimentally against impedance tube measurements and laser vibrometric scans of the cavity-backed panel response. It is shown analytically and experimentally that the air-frame relative velocity is a key factor that alters the input acoustic impedance of thin MPPAs. Coupled mode analysis reveals that the two first resonances of an elastic MPPA are either panel-cavity, hole-cavity, or panel-controlled resonances, depending on whether the effective air mass of the perforations is greater or lower than the first panel modal mass. A critical value of the perforation ratio is found through which the MPPA resonances experience a frequency "jump" and that determines two absorption mechanisms operating out of the transitional region.     

Optimising the absorption and transmission properties of aircraft microperforated panels

A method for evaluating the absorption and transmission performances of multi-layer micro-perforated structures whose facings are excited by different noise sources is described here. It is applied to determine if the acoustical performances of a number of Micro-Perforated Panels (MPPs), optimised both in absorption and transmission, exceed those of typical aircraft panels undergoing internal and external acoustic excitations. A fully-coupled modal formulation is presented that accounts for the effects of the sub-structure volumetric resonances on the acoustical properties of the partitions. It is validated against full-scale measurements performed with a pressure–velocity probe and a laser vibrometer to estimate the absorption and transmission coefficients of single- and double-layer micro-perforated partitions. The model is used to optimise the sound power dissipated by three layouts obtained from a typical aircraft partition by micro-perforating the trim panel (MPP–Porous–Panel), removing the fibreglass material (MPP–Cavity–Panel) and adding a second MPP inside the separating cavity (MPP–MPP–Panel). It is concluded that the MPP–Porous–Panel and MPP–MPP–Panel layouts provide excess interior noise reduction above 1.8 kHz and 1.2 kHz respectively, whereas the MPP–Cavity–Panel is not acoustically more efficient than a typical aircraft panel.     

Estimation of geometric parameters for micro-perforated panels and their effects on sound absorption performance

The geometric parameters of micro-perforated panels with irregular holes cannot be directly known,making it difficult to calculate the sound absorption performance.Therefore,we propose a method of estimating the geometric parameters of micro-perforated panels.The irregular holes are treated as equivalent circular ones,and the model of estimating the geometric parameters is established by using Maa's theory about the panel with circular holes.The result of the parameter estimation of a type of micro-perforated panel is used to predict the absorption performance,resulting in good agreement with experiments.According to the influences of the geometric parameters of the panel on the high absorption region,we discuss the relationship between the application limit of Maa's theory and the geometric parameters,and investigate the evolution law of the sound absorption performance when the panel is polluted by dust.If the parameters of the panel are designed near the center of the high absorption region,large value of the application limit of Maa's theory can be obtained;and if the parameters are located in the upper right part of the high absorption region,a certain degree of dust pollution of the panel does not decrease the sound absorption performance.     

微穿孔板几何参数估算及其对吸声性能的影响

不规则孔微穿孔板几何参数无法直接获知,造成吸声性能计算困难,故提出一种微穿孔板几何参数估算方法。将不规则孔等效处理为圆孔,利用马氏理论关于圆孔微穿孔板的基本理论,建立了微穿孔板几何参数估算模型;将参数估算结果用于吸声性能预测,理论计算与实验结果吻合。根据微穿孔板几何参数对高吸声性能区域的影响,探讨了马氏理论适用极限与微穿孔板几何参数的关系,以及微穿孔板受粉尘污染后吸声性能演变规律。将微穿孔板参数点取在面积较大的高吸声性能区域中间部位,可获得较大的马氏理论适用极限;微穿孔板参数点位于高吸声性能区域右上部位时,一定程度的粉尘污染不会降低吸声性能.      

Feasibility of applying micro-perforated absorbers in acoustic window systems

The paper examines the feasibility of using transparent micro-perforated absorbers (MPA) in a window system to allow noise attenuation whilst at the same time maintaining high levels of comfort ventilation and daylighting. The underlying theory for micro-perforated panels and membranes and the application in silencers is presented. Experiments have been performed between a semi-anechoic and a reverberant chamber using a standard window mock-up, and the effectiveness of MPA has been demonstrated. With a constant air backing, MPA are more effective with a wider ventilation path. With an air flow of up to 2 m/s the performance of the MPA remains unchanged. Current results are based on readily available materials and relatively simple configurations, but the theoretical analysis suggests possibilities for increasing the noise reduction and widening the frequency range by using more strategically designed materials and configurations.